The present application claims priority to Japanese Application No. P11-375013 filed Dec. 28, 1999, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a solid state image sensing device such as a CCD solid state image sensing device and a manufacturing method thereof.
2. Description of the Background Art
In the manufacture of a typical CCD solid state image sensing device, a sensor portion and a CCD transfer channel for photoelectric conversion are formed at a semiconductor substrate, and a transfer electrode/storage electrode of for example polycrystalline silicon is formed in a part including the CCD transfer channel on the semiconductor substrate with a thin insulating film therebetween.
A light shielding film of an Al film for example is formed on the transfer electrode with an interlayer insulating film therebetween, so that light does not come into the transfer electrode and the underlying CCD transfer channel.
However, in order to insulate the transfer electrode/storage electrode and the conductive light shielding film, the interlayer insulating film must have a prescribed thickness, and the presence of the interlayer insulating film creates a gap between the surface of the sensor portion (the surface of the semiconductor substrate) and the light shielding film. As a result, incoming light between the surface of the sensor portion and the lower side of light shielding film leaks into the CCD transfer channel and results in smear.
The smear becomes worse as a function of the thickness of the interlayer insulating film.
Furthermore, a solid state image sensing device having a shunt interconnection connected with a transfer electrode in order to reduce the resistance of the transfer electrode and prevent propagation delay in transfer requires an interlayer insulating film to insulate between the shunt interconnection and the light shielding film. Therefore, the thickness of the insulating film under the light shielding film is even greater. As a result, the smear is worse than the case of the image sensing device without the use of the shunt interconnection.
In order to prevent the smear from becoming worse, a solid state image sensing device has been proposed which is produced by the following process: the transfer electrode/storage electrode and an interlayer insulating film thereon are formed, then an insulating film (oxide film) formed by oxidizing the interlayer insulating film and the substrate surface on the sensor portion is completely etched away, then again the substrate surface is oxidized to form a thin insulating film (oxide film), and an interlayer insulating film having a light shielding film formed thereon is formed on the thin interlayer insulating film.
In this structure, the insulating film under the portion of the light shielding film projecting on the sensor portion is only the thin insulating film formed by oxidizing the substrate surface, so that the gap between the surface of the sensor portion and the light shielding film can be reduced.
This allows the smear to be significantly reduced.
However, the solid state image sensing device having the above structure suffers from the following problems:
(1) A sufficient etching selectivity ratio cannot be secured between the oxide film on the substrate surface and the substrate.
(2) The etching process could damage the substrate. Dark current can be caused if such damage remains on the substrate.
(3) Side etch could be caused at the oxide film at the surface of the transfer electrode/storage electrode at the time of etching the oxide film on the surface of the substrate. If the oxide film on the surface of the transfer electrode is thinned by such side etch, a part of the polycrystalline silicon of the transfer electrode is likely to be oxidized as well in the next step of oxidizing the substrate surface. As a result, the transfer electrode is reduced, and the distance between the transfer channel and the transfer electrode in the substrate is increased, which reduces effective voltage, so that the transfer characteristic and the reading characteristic of pixels deteriorate.
In order to solve the above-described problems, it is an object of the present invention to provide a solid-state image sensing device which allows smear to be reduced and has various characteristics such as transfer and reading characteristics improved, and a method of manufacturing method thereof.
A solid state image sensing device according to the present invention includes sensor portions arranged in a matrix, a vertical transfer register having a transfer electrode provided for each column of the sensor portions, a shunt interconnection of a refractory metal connected to the transfer electrode and a light shielding film covering the transfer electrode. The shunt interconnection and the light shielding film are insulated from one another with an oxide film, an insulating film to serve as a stopper film at the time of pattering the oxide film is provided under the oxide film and the shunt interconnection, and the oxide film and the insulating film to serve as a stopper film are absent under a portion of the light shielding film projecting to the sensor portion side.
A method of manufacturing a solid state image sensing device according to the present invention includes the steps of forming a plurality of sensor portions and a vertical transfer register having a transfer electrode for each column of the sensor portions, forming an etching stopper film of an insulating film on a substrate covering the transfer electrode, forming a refractory metal film on the etching stopper film and pattering the refractory metal film to form a shunt interconnection layer, forming an oxide film on the substrate covering the shunt interconnection layer, etching away the oxide film on the sensor portion using the etching stopper film as an etching stopper, etching away the etching stopper film at least at a part on the sensor portion on the transfer electrode side, and forming a light shielding film covering the surface and forming an opening in the light shielding film on the sensor portion.
In the above-described structure of the solid state image sensing device according to the present invention, the shunt interconnection is formed of a refractory metal, and therefore an oxide film formed at a relatively high temperature can be used for an interlayer insulating film to cover the shunt interconnection for insulation from the light shielding film, so that the use of the oxide film allows the breakdown voltage to be raised.
Furthermore, the insulating film to serve as the etching stopper film at the time of patterning the oxide film is formed under the oxide film and the shunt interconnection, so that the insulating film on the surface of the substrate and around the transfer electrode is not damaged at the time.
In addition, under the portion of the light shielding film projecting to the sensor portion side, the oxide film and the insulating film to serve as an etching stopper film are not formed, so that the gap between the sensor portion and the projecting portion of the light shielding film can be reduced, and incoming leakage light which causes smear can be reduced.
By the manufacturing method according to the present invention, the etching stopper film of an insulating film is formed on the substrate covering the transfer electrode, and therefore the insulating film on the surface of the substrate or around the transfer electrode can be protected against damages by the etching stopper film at the time of pattering an oxide film to be subsequently formed.
The refractory metal film can be patterned to form a shunt interconnection layer, and therefore an oxide film formed at a relatively high temperature can be used for an interlayer insulating film covering the shunt interconnection for insulation from the light shielding film.
The use of the oxide film formed covering the shunt interconnection allows the breakdown voltage between the shunt interconnection and the light shielding film to be raised.
Furthermore, the oxide film on the sensor portion is etched away, then the etching stopper film is etched away at least at a part on the sensor portion on the transfer electrode side and a light shielding film having an opening on the sensor portion is formed, so that at the portion of the light shielding film projecting onto the sensor portion on the opening side, the light shielding film is formed after the oxide film and the etching stopper film are removed, and the gap between the projecting portion of the light shielding film and the sensor portion can be reduced.